Recent Space and ground based telescope have opened new windows of observation for wavelengths ranging from far infrared to sub-millimeter with spatial and spectral resolutions previously unmatched. To make the most of these observations, an accurate knowledge of the physical and chemical processes occuring in the inter- stellar medium (ISM) is essential. In this presentation, I will show what are the current needs in astrophysics in terms on molecular data and how accurate data are a crucial parameters for the determination of physical conditions in molecular clouds.